As President Joe Biden wraps up a separate visit to the region that included his first in-person meeting as president with Chinese leader the Vice President left for Southeast Asia.
Harris' trip to Thailand and the Philippines will include a visit to the southern Philippine island of the same name.
The vice president is the highest-ranking US official ever to visit Palawan, according to a senior administration official.
The eastern edge of the South China Sea is where China has built military outposts and made aggressive claims that have worried its neighbors and the United States.
Harris will travel to the Philippines on Monday to meet with her counterpart and the president of the country.
The official said that Harris would focus on "strengthening our security alliances and our economic relationship."
Harris intends to "reaffirm our defense commitments to the Philippines and the importance of our alliance and peace and stability in the South China Sea," according to the official.
On November 22, Harris will meet with residents, civil society leaders, and representatives of the Philippine Coast Guard to demonstrate the US's commitment to stand with the Philippine ally in uphold the rules-based international maritime order in the South China Sea.
The largest province in the Philippines is Palawan, which spans from the central Philippines to Malaysia's northeastern tip on the island of Borneo. The Philippines is one of several countries that dispute Beijing's expansive claims.
It's important because it's close to some of the key Chinese artificial island outposts in the Spratlys.
The Chinese military could use the straits between the seas to move around the area.
Compared to bases in the north of the Philippines, staging air and naval operations out of Palawan saves time and money.
Ten years ago, Washington and Manila agreed to expand the US presence and support other projects at some Philippine military bases. The work was delayed because Marcos' predecessor was more friendly to the US.
Manila said this week that work on agreed-upon projects would be done in the next few years. The chief of staff of the Philippine military said this week that the US was interested in more projects.
The emphasis of the US has put on maritime security, particularly on combatting illegal, unregulated, and unreported fishing, for which it says China is the worst offenders, is reflected in Harris' trip.
At the US-ASEAN summit in May, Harris announced $60 million for new US Coast Guard-led maritime initiatives in the region.
Harris will see firsthand the outcomes of the partnership and discuss how to strengthen it even further with new funding and initiatives.
There is a dispute between the Philippines and China over the South China Sea. The navy ship was grounded in 1999 to mark the claim. There is a small contingent of troops at the outpost. China wants Manila to remove the ship and is trying to block the missions.
In Japan in September, Harris said China was using its military and economic heft to "coerce and intimidate its neighbors," and her visit to Palawan now, shortly after Biden and Xi's meeting, may hurt Beijing.
The US official said that China could take the message it wants. The United States is a member of the Indo- Pacific. We're going to get married. The security of our allies is a priority for us.